XP Logon: Password sometimes not accepted - have to reboot requent

techsc

A very strange behaviour on my Laptop:

On the welcome screen, XP sometimes tells me that the entered password is
wrong - which is definitely not the case.

I have to reboot multiple times to get XP accepting my password again.
During these reboots it sometimes happens that the whole username (an
eventually all other login names) is removed from the Welcome Screen.

The behaviour seems to be connected with the resume from standby/hibernation
and the clean boot on battery only - I'm not kidding: The problem mostly
happens if I boot on batteries only. When connected to the power chord the
problem never arised.